1. Field of the Invention
The present invention relates to recording media such as an optical disk with a data format that is a data structure in recording/reproducing multi-level data.
2. Description of the Related Art
Conventionally, a recording medium having the following data format has been proposed: an optical disk having the data format of an optical disk “DVD” and recording data by performing 8/16 modulation that converts 8-bit data into 16-bit data. An ECC (Error Correction Code) block format for error correction includes user data of 2048 bytes in one sector, and 16 sectors constitute one ECC block. In addition, a product code is used for error correction, and one ECC block is formed by 182×208 bytes of data with 208 rows of 182-byte lines. There are 10 bytes of PI (Parity of Inner code) parity data according to Reed-Solomon code RS (182, 172, 11) in the row direction, and 16 bytes of PO (Parity of Outer code) parity data according to RS (208, 192, 17) in the column direction (refer to ‘DVD Physical Format’ PIONEER R&D 1996 Vol. 6 No. 2 (13th issue): Special Topic “DVD” p.7–p.14, and ‘An outline of the 8/16 Modulation’ p.32–p.36, for example).
The recording medium with the format as described above, however, has a disadvantage in that the format efficiency (the ratio of the amount of user data to the amount of total data to be recorded) is low, as shown below:
(1) format efficiency of the 8/16-modulation method=0.5×(1456 bits/1488 bits)=0.489
(2) format efficiency of ECC block=2048 bytes×16 sectors/182 bytes×208 rows=0.866
(3) total format efficiency=format efficiency of 8/16-modulation method×format efficiency of ECC block=0.423
Especially, unlike the data formats of such as conventional DVDs where all data are constructed by binary data, a data format including multi-level data requires a new process of converting multi-level data into binary data. It is necessary to devise a data format so as to avoid waste (inefficient utilization) of data capacity in the conversion process.
In addition, while user data are generally constructed by 8 bits, the unit of multi-level recording is not 8 bits. Thus, when a format is formed with 8-bit units, inefficiency is caused such as one error on the medium becomes a two-word error in relation to the conversion.